During the operation and decommission of the pressurized water reactor nuclear power plant equipments, a large number of high level boron containing radioactive waste ion exchange resins (hereinafter referred to as waste resin) will be generated, under dry state, the appearances of the waste resins are granular pellets or powders, and if there is no storage container, the waste resins are easily dispersed, upon soaking with water, the radionuclides exchanged and entrained on the waste resins will be desorbed, polluting the environment, thus causing a secondary pollution. The specific gravities of the waste resins are 1.05-1.30, slightly higher than water, when the water content or the resin types and the adsorbed ions are different, the specific gravities of the waste resins are varied. The bulk density of the waste resin in water is 0.65-0.85 g/ml. Upon the water unsaturated waste resins contacting with water, they will absorb water and generate volume expansions, during drying and dehydration, the volumes are reduced, thus having a large volume change. These resins are difficult to regenerate, and it will produce a large amount of radioactive waste water in the regeneration, so they must be properly disposed to reduce their potential environmental hazards. Cement has excellent physical, chemical and mechanical properties, it is a good matrix material for solidifying the radioactive wastes. The solidifications of low and intermediate level radioactive wastes generally adopt the cement solidification, which is a mature treatment technology, also one of the earliest applied radioactive waste treatment technologies. In this treatment, the radioactive liquid wastes or radioactive solid wastes are mixed with cement, water, additives, etc., in a certain proportion, and the mixture is hardened into a waste solidified body at room temperature.
The cement solidified body retains the nuclide ions in the cement solidified body by means of such effects as mechanical sealing, matrix adsorption, solid solution, etc., and the performances of the cement solidified body depend on the chemical composition, physical structure, and the external environment of the cement solidified body. Upon adding water, the cement changes gradually from a slurry with plasticity and fluidity to a solid with a certain strength. The hardened cement slurry is a non-homogeneous multiphase system, which consists of solid phase materials composed of a variety of hydration products and the residual clinkers, and the liquid and air present in the pore spaces. When there are no morphology changes, the ion exchange resin has a considerable chemical stability, the matrix itself is incompatible with the cement, and the cement only plays an embedding effect. However, the major chemical substances adsorbed by the waste resins will be desorbed continuously, and some substances will have a great effect on the cement hydration reaction, causing the cement slurry quick-condensing or slow-condensing, wherein the severe slow-condensing will result in a complete non-condensing. For example, the objects to be treated by the present application, i.e. the high boron containing waste resins, if treated with the existing cement solidification agents, the cement slurry non-condensing phenomenon will occur because borates are the commonly used cement retarders.
Upon the cement solidification of the waste resins, the resins are embedded in the cavity of the solidified body, i.e., the whole solidified body has a cage-like structure. The cement composition, the forming water-cement ratio and the forming conditions together determine the microporous structure of the cement solidified body, and the microporous structure in turn determines almost all of the physicochemical properties of the cement solidified body, such as density, strength, thermal property, durability and the like. The radionuclide ions can diffuse into the external medium via the communicating micropores in the cement solidified body. Numerous studies show that, during the cement solidification, the type and amount of the cement, the property and amount of the resin, the additive composition, the water-cement ratio, the solidification operation process, etc., have a great effect on the performances of the solidified body. When the formulation is unreasonable, the cement solidified body has a high enlargement ratio, upon contacting with water, it will expand and generate cracks, or even broken, thus the leaching rate of the radionuclides is high, which cannot achieve the performance index of the cement solidified body specified in the National Standards. Additionally, in this field, the containment rate to the waste resins of about 50% water content is typically less than 40%, the lower containment rate will increase the waste production and waste disposal costs, wherein the containment rate refers to the percentage of the contained substances in the total volume of the containing substances.
In the existing waste resin cement solidification techniques, many of them still use zeolite as an additive to reduce the consumption of cement, when other aggregate such as sand is not used during solidifying the waste resins, the proportion of the cement used is high, thus a high hydration heat phenomenon appears, in the bulk concretes, the high hydration heat will result in the core temperature of the waste resin solidified body excessively high, thus causing the solidified body expanding and reducing the performances of the waste solidified body. As for the solidification process using, for example, sulphoaluminate cement, which has a high hydration heat and an intensive release time, adding zeolite is an effective control method, which is commonly used in the preparation of the conventional concrete for controlling the hydration heat. However, the solidification of the high level boron containing radioactive waste resins is different from the preparation of the general concrete, as well as the solidification of the general radioactive waste resins, because the high level boron containing radioactive waste resin liquid wastes contain a large amount of borate ions and other anions and cations adsorbed in the ion exchange resin, upon the cement solidification, the borate ions and the anions and cations desorbed from the ion exchange resin change the chemical properties of the cement solidified body, so that upon zeolite, used as an additive, reaching a certain amount, the performances of the cement solidified body will be reduced, even upon the cement solidified body contacting with water, the solidified body is pulverized.
In addition, a large amount of borate ions contained in the high level boron containing resins, result in a long condensation time during the cement solidification, which has a great effect on the performances of the cement solidified body, it is possible to cause such problems as non-condensing of the cement slurry, low strength of the cement solidified body and floating and delamination of the resins, etc., this is the reason why the compositions of many existing cement solidification formulations are partly identical, but they cannot be directly used for the cement solidification of high level boron containing waste resin.